The present invention is directed to control devices for bicycles and, more particularly, to a twist-grip shift control device for shifting a bicycle transmission.
An example of a twist-grip shift control device is shown in U.S. Pat. No. 5,921,139. That shift control device comprises a fixed member that is nonrotatably fixed to the bicycle handlebar, a handgrip operating member rotatably supported relative to the fixed member for rotating in first and second directions, a takeup member rotatably mounted relative to the fixed member for controlling the pulling and releasing of a transmission control element, and an intermediate (position setting) member coupled for rotation with the takeup member. Ratchet teeth are formed on the fixed member and the intermediate member for holding the intermediate member, and hence the takeup member, in a plurality of fixed positions. Additional ratchet teeth are formed on the intermediate member and the handgrip operating member for rotating the intermediate member and the takeup member for pulling and releasing the transmission control element.
Twist-grip shift control devices have long been used to control bicycle transmissions such as derailleurs and internal hub transmissions. In derailleur transmissions, it is sometimes desirable to provide an overshift function when shifting from one sprocket to an adjacent sprocket. When performing this function, the derailleur chain guide temporarily moves the chain beyond the destination sprocket to ensure that the chain has engaged the destination sprocket and then returns the chain into proper alignment with the destination sprocket. JP 1969-26571 and U.S. Pat. No. 5,102,372 both disclose twist grip shifting devices that perform this function. In JP 1969-26571 a spring-biased ball moves within a space to provide the overshift function, whereas in U.S. Pat. No. 5,102,372 a leaf spring moves within a space to provide the overshift function.